No abstract

Loss of genetic variability can be detrimental to a population's survival traits and ¢tness. These e¡ects are likely to be maximized in shrimp closed broodstock rearing systems where post-larvae are often produced from crosses of breeders collected from an associated grow-out farm after mass selection. Longtime broodstock management in closed systems is also expected to lead to reduction in or even complete eradication of genetic variability. The present work aimed at monitoring the genetic variability of a Litopenaeus vannamei hatchery in the state of Pernambuco (Brazil), during three successive replacements, using microsatellite markers. No signi¢cant genetic diversity losses have been observed through the values of mean heterozygosity (H o 5 0.460 and H e 5 0.660 in the ¢rst sample; H o 5 0.420 and H e 5 0.620 in the second sample; and H o 5 0.600 and H e 5 0.660 in the third sample). However, some alleles appear to have been lost after three replacements. The diversity level was considered to be high and is comparable to those reported for wild populations, suggesting that the original imported founder stock of Brazilian L. vannamei is likely to have had a high genetic diversity, possibly due to multiple origins.

Two migratory and endangered freshwater fish species, Salminus franciscanus and Brycon orthotaenia, are endemic to one of the most important basins for hydropower capacity in South America. These two fish are target species of conservation aquaculture programmes along the São Francisco River system. In order to implement effective strategies for the conservation of these species, microsatellite markers were developed and used to assess the genetic diversity and structure among wild groups. Fish were collected during the spawning season at four sampling sites, covering more than 1000 km. Polymorphism loci were assessed, and a total of 133 and 107 alleles were found for S. franciscanus and B. orthotaenia, respectively. Despite the critical conservation status, B. orthotaenia showed high levels of genetic diversity, comparable with those of other closely related species. Salminus franciscanus exhibited half of the genetic diversity of its sister species in terms of allelic diversity, indicating that this species will be more prone to genetic drift and inbreeding in conservation aquaculture programmes. The results of an analysis of molecular variance for microsatellite markers in these species (FST = 0.007 for S. franciscanus and FST = 0.003 for B. orthotaenia) and the estimated recent migration rates (>40% among sampling sites) support panmixia in both species, despite the heterogeneities of the riverscape. The results of this study and the microsatellites developed will play an important role in assisting agencies in making informed decisions on conservation aquaculture programmes.